I have the FaxPro commercial module licensed and installed.
I am observing the same weird error message when receiving a fax from two different sip providers.
One supports T.38 and ones does not.
The error message appears three times in a row as follows:
[2017-01-16 15:18:59] WARNING[15621][C-00000008]: res_fax_spandsp.c:438 spandsp_log: WARNING T.30 ECM carrier not found
[2017-01-16 15:19:00] WARNING[15621][C-00000008]: res_fax_spandsp.c:438 spandsp_log: WARNING T.30 ECM carrier not found
[2017-01-16 15:19:00] WARNING[15621][C-00000008]: res_fax_spandsp.c:438 spandsp_log: WARNING T.30 ECM carrier not found
I tried turning ECM on and off but it made no difference.
I also tried forcing only ulaw for the extensions and trunks that use the fax module.
It just started appearing recently but I cannot say if it was after a specific module or asterisk update or not.